"Active" lightwave circuits or networks typically include electrical or electromechanical switches that can cause a change in state in the network. Such a change in state is used, for example, to control information flow throughout the network. The switches used in such circuits require power for actuation, which is typically supplied by external electrical sources over copper wire. Terminals, repeaters and remote node sites in the lightwave circuit must therefore be wired so that power can be delivered to switches resident at such locations.
In many networks, providing electrical service in the aforedescribed manner is impractical or too costly. Moreover, due to the presence of active devices (e.g., the switches), field-deployed active lightwave circuits are likely to experience reliability problems and high maintenance costs. Passive lightwave systems are an alternative; unfortunately, such passive systems tend to incur added complexity at terminal sites to compensate for the limited functionality outside the terminal sites.
Optically-powered circuits can enhance the functionality of an otherwise passive optical system. In such circuits, power is supplied by an optical beam rather than an external electrical source. In some optically-powered circuits, the optical beam powers a photogenerator that produces a current/voltage to drive an electromechanical or electrooptical device. For example, a micro power stepper motor switch powered by an indium gallium arsenide (InGaAs) photogenerator has been remotely actuated through 100 km of transmission fiber. See, Dentai et al., "High-Voltage (2.1V) Integrated InGaAs Photo-generator," v. 33, no. 8, Elect. Lett., pp. 718-19, 1997; and U.S. Pat. No. 5,714,773 to Burrows et al.
The photogenerators used in such lightwave circuits can be categorized by the wavelength of the illuminating beam. Short wave photogenerators are powered by light having a wavelength less than about 950 nanometers (nm), and long wave photogenerators are powered by light having a wavelength greater than about 1200 nm. Short wave photogenerators are capable of generating more current and voltage than long wave photogenerators. To satisfy the non-negligible current and voltage requirements of the electrical and electromechanical devices used in prior art optically-powered circuits, short wave photogenerators are typically used.
Unfortunately, the "short" wavelength light that powers short wave photogenerators is subject to significantly higher attenuation in optical fiber than the "long" wavelength light that powers long wave photogenerators. As a result, a fiber run to a remote node at which a short wave photogenerator and switch are located is typically limited to a significantly shorter length than if a long wave photogenerator was present at the node. To extend the length of the fiber run, a higher power optical beam must be launched into the fiber. Aside from the increased power requirements associated with such a higher power beam, there is an increased likelihood and severity of cross talk between the power beam and the information-carrying optical signals being delivered to the node. In addition to the aforementioned drawbacks, prior art active lightwave circuits typically suffer from a relatively low bandwidth and long switching times.
The art would thus benefit from an optically-powered circuit that uses long wave photogenerators to provide power for actuating switches and the like.